STABILISED FABRICS AND REINFORCED PRODUCTS CONTAINING THEM

Abstract: A bonded fabric comprises a mesh of filaments of the core-sheath type, the fabric having substantially no elasticity in the longitudinal direction under first conditions, but whose bonding is capable of breaking or yielding under second conditions without affecting the relatively strong filament cores. This fabric can be used to reinforce a hose or similar matrix, in which the bonding breaks when the product is flexed.

Description: STABILISED FABRICS AND REINFORCED PRODUCTS CONTAINING THEM Field of the Invention This invention relates to textile fabrics of the type commonly used in industrial applications as a reinforcement of products including radiator, fuel filler and other hoses. The invention relates also to the reinforced products and to their manufacture. Background of the Invention Most woven fabrics used in industrial textile applications have a load-bearing warp and weft and will therefore not distort if tensioned in either direction. However, some textile fabrics such as Atlas-stitch knitted fabrics are dimensionally less stable once they are released from the control mechanism of their production machines, and will easily distort when tensioned in the longitudinal or transverse direction. Such fabrics are sometimes preferred as reinforcing materials because they 'facilitate shaping during manufacture of a composite product, e.g. a radiator hose. An automobile radiator coolant hose and a method for its production are disclosed in US-A-4242296. It is apparently the case that the reinforcing fabric allows the hose material to be deformed to a limited extent only. The hose is produced by using a first extrusion head, for obtaining an inner hose portion onto which the reinforcing fabric is applied, and a second extrusion head for producing an outer hose portion on the fabric. When the second hose portion is applied, the fabric stretches. When the hose material is bent, the reinforcing fabric can be stretched only to a limited extent, so that the bending radius must be large. EP-A-0100573 describes a method for shaping a hose of material including a reinforcing fabric, and curing the material in the desired shape. However, it appears that, when the hose is bent, the fabric will not stretch as much as might be desired and will therefore tear, whereupon the wall of the hose may also tear/burst at the outside of the bend. If the reinforcing fabric does not tear, the inner side of the bend will fold: the internal cross-section of the tube is therefore distorted, to give an oval cross- section at the bend. If a conventional reinforcing fabric can be stretched in the longitudinal direction sufficiently to allow bending of the hose, the likely result is that the fabric will stretch during production of a hose, resulting in a change in fabric orientation. The fabric's tensile strength or width may thus be changed undesirably, e.g. by reducing or removing the overlap between the edges of a fabric defining an annulus in a green hose, thus affecting the properties of the product when shaped. In other words, the fabric will not have the desired degree of dimensional stability. EP-A-0425099 describes a fabric which can withstand the forces applied to it when incorporated as a reinforcement in a composite product, which is stretched to a limited extent only during this procedure, but which allows the product to be bent into a desired shape, while retaining its reinforcing function. That fabric is stabilised by means, e.g. longitudinal filaments, which are breakable or otherwise capable of losing their stabilising effect. The reinforced product is produced from a fabric which is dimensionally-stable, and is then treated or otherwise handled to destroy the stabilising means in situ, and give the advantage of easy shaping. The fabric does not distort during slitting and incorporation into a matrix, while the reinforced product can be shaped without deformation, e.g. buckling or tearing. Various materials are suggested in EP-A-0425099, for constructing the fabric and stabilising filaments. Various mesh fabrics that are woven or knitted are described, although one suggestion is that for an aramid material, which is less suitable to be looped, the fabric may comprise a bonded mesh of linear filaments ana, if desired, stabilising carrier threads that are stitched in. It has been found, however, that the mere bonding of filaments may not overcome the problem of distortion described above. Further, the looping of filaments means increasing the thickness of the reinforced product. This is undesirable because, in order that the matrix covers the entire fabric, the use of silicone rubber or other expensive matrix materials is uneconomic despite their other advantages. Summary of the Invention According to the present invention, a bonded fabric comprises a mesh of filaments of the core-sheath type, the fabric having substantially no elasticity in the longitudinal direction under first conditions, but whose bonding is capable of breaking or yielding under second conditions without affecting the relatively strong filament cores. This fabric has essentially the same reinforcing function as that described in EP-A-0425099 and comprising stabilising longitudinal filaments. In accordance with the present invention, the filaments are usually linear and any longitudinal filaments are relatively thin. In consequence, the thickness of the fabric is largely determined by the thickness of the mesh filaments. A further advantage of the novel mesh fabric is that it can be conveniently produced, e.g. with longitudinal filaments providing plain selvedges, on a tape machine. Detailed Description of the Invention The mesh filaments are not restricted by their tendency to undergo abrasion if looped. Suitable core materials can therefore have a very high tensile strength, examples being polyamide, silica, polyester, aramid, glass and carbon fibres. The core often has a specific gravity of at least 1, e.g. 1.2 to 1.5, g/cm (1.38 for polyester) . The sheath material and any longitudinal filament or carrier thread may be a filamentary material of relatively low but sufficient strength to carry the fabric through slitting and the production of, say, a green (i.e. uncured) hose, without distortion. When the stabilised fabric is incorporated into a composite product that requires shaping, e.g. a radiator coolant hose, the bonding or stabilising effect is capable of breaking or passing its yield point, if appropriate on heating, thus enabling the shaping action to take place. One way in which the reinforcement may be produced is to spin, core-texture, envelope or twist around a yarn such as glass, aramid or carbon, another yarn or foil with a lower melting point than the main reinforcement yarn. Preferably, the core yarn (whether or not composite itself) is passed through a solution of a thermoplastic material such as polyamide, polyethylene, polypropylene or other polyolefin, PVC, polyacrylate, PET or PEBT. In this way, the construction of the core yarn is maintained. A composite fabric may then be made by applying heat, pressure or other means, so that the matrix yarn or coating melts together with the surface of other laid-in ends. The binding can be sufficient so that a longitudinal carrier yarn may not be necessary. The heat/pressure or other means will make the binding sufficient to get through the process. Also, by applying a higher force than used during the production process, the, say, green hose reinforcement fabric will allow the shaping as the connection points will yield. This technique can also be used to reduce the abrasion of yarns such as aramid, glass or carbon, and to increase the impact resistance and to increase the adhesion to the rubber. A typical yarn is a glass yarn with polyamide around or an aramid with e.g. polyamide around. The amount of matrix yarn around the reinforcement is usually 5% to 60%, preferably 15% to 40% by weight. Adhesive-bonding of the mesh fabric may be particularly preferred when longitudinal filaments are present in the form of selvedge yarns. While such a yarn may be thinner than the mesh filaments, a primary object of a mesh that, at least in its central, crossing-point area, it is relatively thin (e.g. less than 1 mm) and easy to produce, can also be met if the selvedge yarn, of any suitable type, is thicker (in which case the fabric may have enhanced bursting strength) . The selvedge may be glued, stitched or otherwise bound to the mesh fabric, but is preferably a normal plain selvedge. A fabric-reinforced, stabilised product of the invention may be made by generally known techniques, e.g. the separate extrusion of two layers of extrudable matrix material and the insertion therebetween of the reinforcing fabric. The product is preferably in the form of a tube or hose, but it will be apparent that the invention is equally applicable to the production of other products, such as cables, upholstery, boots or other footwear, roofing or tent reinforcement, and bicycle or other tyres. In general, the invention is appropriate for use in cases where the product has to be bent through an arc or otherwise deformed into a desired shape. Shaping may be sufficient to provide a stable product: if necessary, curing or vulcanisation may follow. By way of example, a hose of the invention may be produced by extruding material from first and second coaxial extrusion heads, and continuously supplying a strip of stabilised reinforcing fabric between the heads. The strip is applied so that its longitudinal edges are contiguous or overlapping, the strip being applied onto the inner layer of extruded material. The reinforcing fabric should preferably have a sufficiently open structure that the material or materials extruded through the coaxial heads can flow together through the fabric. The stabilised reinforcing fabric has a modulus of elasticity which is relatively high, and thus a low degree of stretch, e.g. under tension up to a certain value. When the tension exceeds this value, the bonding means may break or deconstruct, or the modulus of elasticity may be relatively low, and the fabric can therefore be relatively easily stretched. Initially, the fabric will maintain its shape when a force is applied in the longitudinal direction of the hose. When the hose is bent, the fabric is under strain at the outside of the bend, such that the stabilising means will be destroyed or deconstructed, or become yielding, so that the fabric can be stretched together with the material of the hose. Neither the bas.e fabric nor the wall of the hose tears. The cross-section and stability of the hose are maintained. The low elasticity exists for the fabric per se, and is retained over a range of conditions including slitting and bonding to a curable rubber or plastics matrix. This effect is reduced or removed under different conditions, e.g. under tension, but without affecting the integrity of the mesh. Therefore, after application of these different conditions, the fabric essentially comprises only, or essentially only, the core filaments. If the stabilising means is broken or otherwise deconstructed, or yields, under tension, the relative melting points of the core and sheath materials are not critical. However, if the bonding means is a material that is not breakable or yielding, its melting point should be lower than that of the mesh fabric. In particular, the reinforcing fabric can be in the shape of a lay-in, knitted or braided fabric with an open structure and with meshes in the shape of a rhombus, parallelogram or other rectangle; opposing corner points of succeeding meshes lie on a line which, when the fabric is laid in the hose material, extends substantially parallel to the longitudinal direction of the hose, and may be connected by longitudinal threads. These threads effect their connecting function as long as this is necessary, especially during slitting the fabric and a green hose production process. In the case of a composite mesh fabric, the sheath functions to bond the fabric, rather than longitudinal filaments. In general, it is preferred that the meshes are defined by sides making an angle of 40° to 80°, e.g. 40° to 70°, preferably 45° to 65°, e.g. about 55°, with the longitudinal direction of the fabric and of a hose or other product including the fabric. For the purpose of illustration, reference may be made to Figures 1 and 2 of the drawings in EP-A-0425099. Figures 6 and 7 in that specification illustrate the theory underlying the utility of reinforced fabrics of the type described there and of this invention. The following Examples illustrate fabrics of the invention. Each may be used to reinforce a coolant hose as described in Example 1 of EP-A-0425099. Example 1 A mesh fabric is made from 840 den Aramid yarn (8 turns per meter; mesh angle 63°C) . The fabric contains 3 ends per inch (25.4 mm) of Aramid reinforcement yarn with 2 selvedge ends (1 on each side) of 940 dtex PA66 and 23 light longitudinal carrier yarns in 78 dtex PA66. These carrier yarns are laid between 2 layers of reinforcement yarns. The selvedge yarn provides a smooth selvedge, prevents the Aramid y&rns cutting each other, and increases the hose strength. The fabric is kept together by a dip in RFL which promotes at the same time the adhesion, to the matrix (in this case: rubber). The dip may also replace, partially or entirely, the carrier ends. Example 2 A fabric (150 mm wide) is produced from 940x2x2 PA66 as reinforcement with 11x2 carrier ends of 78 dtex PA66 and 2 selvedge ends of 280 dtex PA66. The reinforcement has 10 ends per 10.2 cm; the mesh angle is 45°C. The nylon 940/2/2 has 100 t/m Z and 100 t/m S. The longitudinal ends have a twist of 295 t/m. The whole is dipped in and kept together by RFL. Example 3 A fabric (140 mm wide) is composed of a glass yarn (1360 dtex reinforcement) covered with a 1100 dtex polyester yarn, making up a total of 2460 dtex. The fabric has a 550 dtex polyester selvedge yarn and is kept together by the application of heat and pressure. The fabric has 4 ends per inch (25.4 mm). The mesh angle is 54°C. Example 4 A fabric (130 mm wide; mesh angle 54°C) is made of a glass 1360 dtex yarn, with selvedge ends of polyolefine 550 dtex. It is passed through a polyolefine solution, and contains no carrier ends. The polyolefine provided sufficient stability together with the selvedge yarns. The temperature and pressure are set such that this connection will be released at the required bending forces.

Claims: CLAIMS 1. A bonded fabric comprising a mesh of filaments of the core-sheath type, the fabric having substantially no elasticity in the longitudinal direction under first conditions, but whose bonding is capable of breaking or yielding under second conditions without affecting the relatively strong filament cores. 2. A fabric according to claim 1, in which the mesh is bonded together at the crossing points of the filaments. 3. A fabric according to claim 1 or claim 2, additionally comprising longitudinally-extending filaments. . A fabric according to claims 2 and 3, in which the longitudinal filaments are sewn, tufted, stitched, bonded or knitted around the said crossing points. 5. A fabric according to claim 3 or claim 4, in which the longitudinal filaments provide a plain selvedge. 6. A fabric according to any preceding claim, in which the second conditions comprise heat, irradiation or tension. 7. A fabric according to any preceding claim, which is less than 1 mm thick. 8. A product reinforced by a fabric according to any preceding claim, as obtained by reinforcing the product matrix with the fabric under the first conditions, and then subjecting the reinforced product to the second conditions. 9. A product according to claim 8, which comprises a rubber or plastics matrix containing the fabric. 10. A product according to claim 9, in which the matrix comprises a silicone or EPDM rubber. 11. A product according to any of claims 8 to 10, in the form of a shaped hose. 12. A method for producing a product according to claim 11. which comprises extruding inner and outer layers of extrudable material through coaxial extrusion heads, and applying the reinforcing fabric therebetween, under the first conditions; and shaping the fabric-reinforced hose under the second conditions.

Inventors: DE MEYER WILLY, DE MEYER, WILLY
Applicants: MILLIKEN EUROP NV, MILLIKEN EUROPE N.V.
Application year: 1994
Main classification: B29C67
IPC codes: B29C47, B29C70, B29L9, B29L23, D03D1, D03D15